Arrangements are known wherein a beam generated, for example, by a Nd/YAG laser is utilized in order to machine a workpiece. This machining can be carried out as boring, cutting or welding of the workpiece depending upon the energy density of the laser beam at the point of incidence.
Splatterings of the particular material are produced during all of these machining processes and are hurled also in the direction of the laser source. Since these material splatterings can contaminate the sensitivity of the laser optics, an exit window arranged between the workpiece and the laser is customarily utilized. The exit window shields the laser against splatterings of the material.
Such an exit window is made of glass and can be provided with a layer which increases the transmission. Exit windows of this kind are relatively expensive since their surfaces must be mutually parallel to a high degree of precision in order to prevent disturbing optical influences.
It has been shown that metal splatterings burn into an exit window made of glass, for example, when welding metal. In this way, conchoidal fractures develop in the glass. This dirtying of the exit window effects changes and distortions of the laser beam passing through the window since the cross section of the beam is small compared to the magnitude of the resultant contaminations.
In arrangements for welding metals and especially for spot welding by means of a laser beam, the contaminations of the exit windows lead to gradual reductions in quality as a consequence of the laser beam being optically influenced. With automatically driven equipment, these quality reductions can only be recognized during a later examination of the workpiece.
Previously, it was the practice to limit the service life of the exit windows in order to limit the number of such defective weldings. This leads to the situation that the exit windows have to be exchanged after only a few hours of operation.
The frequent interruptions in production caused by this exchange of exit windows leads to an increase in the cost of production which is further increased by the cost of the substitute windows.